Patent document 1 proposes a light shielding film used for a window material or the like, containing a black pigment including an inorganic pigment such as carbon black and titanium black having absorption in a region from visible light to near-infrared light, and an organic pigment such as aniline black having strong absorption only in a visible light region. Patent document 2 proposes a half-mirror type light shielding member, which is vapor-deposited with metal such as aluminium.
Patent document 3 proposes a heat ray cut-off glass suitably used at a position requiring high visible ray transmission, having an excellent heat ray cut-off performance, in which a multiple tungsten oxide film as a first layer is provided incorporating at least one kind metal element selected from the group consisting of group IIIa, Iva, Vb, Vib, and VIIb in periodic table, from a substrate side on a transparent glass substrate, and a transparent dielectric film as a second layer on the first layer, and the refractive index of the transparent dielectric film of the second layer is made to be lower than the refractive index of the multiple tungsten oxide film of the first layer or the third layer.
In the same method as that of the patent document 3, patent document 4 proposes the heat ray cut-off glass by laminating the first dielectric film on the glass substrate as the first layer from the substrate side, the tungsten oxide film thereon as the second layer and the second dielectric film further thereon as the third layer.
In the same way as the patent document 3, patent document 5 proposes the heat ray cut-off glass by laminating the tungsten oxide composite film containing the same metal element as the first layer from the substrate side, and laminating the transparent dielectric film on the first layer as the second layer.
Patent document 6 proposes a coated glass sheet for controlling solar light having a solar light-shielding characteristic. This glass sheet is formed by coating a film of a metal oxide by a CVD method or a spraying method and subjecting the film to thermal decomposition at about 250° C. The metal oxide is at least selected from the group consisting of tungsten trioxide (WO3), molybdenum trioxide (MoO3), niobium pentaoxide (Nb2O5), tantalum pentaoxide (Ta2O5), vanadium pentaoxide (V2O5) and vanadium dioxide (VO2) containing additives such as hydrogen, lithium, sodium and potassium.
Patent document 7 proposes a photochromic, heat-insulative material that can undergo rapid coloration/decoloration processes upon exposure to the sunlight and that, when colored, has an absorption peak at 1250 nm and can thus shield the sunlight in the near-infrared region. This material uses a tungsten oxide obtained by hydrolysis of tungsten acid. A specific organic polymer called polyvinylpyrrolidone is added to the tungsten oxide. When the material is exposed to the sunlight, UV-rays contained in the sunlight are absorbed by the tungsten oxide. This results in the generation of excited electrons and holes. As a result, a small dose of UV irradiation can cause the generation of a significant amount of tungsten with a valency of 5, which accelerates the coloring of the material. As the color density of the material increases, the material shields a significant proportion of the sunlight, and the tungsten with a valency of 5 is immediately oxidized to a valency of 6. This in turn causes rapid fading of the color of the material.
The present inventors in Patent document 8 propose a way to obtain tungsten trioxide, a hydrate or a mixture thereof. Specifically, tungsten hexachloride is dissolved in an alcohol. A desired product is given by evaporating the solvent from the mixture, or first refluxing the mixture and then evaporating the solvent, followed by heating the residue at 100° C. to 500° C. The present inventors also propose that fine particles of such a tungsten oxide can be used to fabricate an electrochromic element to form a multi-layer laminate, and when introducing protons in the film, optical characteristics of the film can be changed.
Patent document 9 proposes a method for producing various tungsten bronzes as expressed by the formula: MxWO3 (where M is a metal element, such as an alkali metal, alkaline earth metal or rare earth metal; satisfying 0<x<1). This method uses an ammonium meta tungstate and various water-soluble metal salts as starting materials and involves heating an aqueous solution of the reactants at about 300 to 700° C., drying the aqueous mixture to obtain a solid product, and supplying a gaseous hydrogen containing an inert gas (in an amount of approx. 50 vol % or more) or water vapor (in an amount of approx. 15 vol % or less) to the solid material.
[Patent document 1] Japanese Patent Laid-Open Publication No. 2003-029314
[Patent document 2] Japanese Patent Laid-Open Publication No. Hei 9-107815
[Patent document 3] Japanese Patent Laid-Open Publication No. Hei 8-59300
[Patent document 4] Japanese Patent Laid-Open Publication No. Hei 8-12378
[Patent document 5] Japanese Patent Laid-Open Publication No. Hei 8-283044
[Patent document 6] Japanese Patent Laid-Open Publication No. 2000-119045
[Patent document 7] Japanese Patent Laid-Open Publication No. Hei 9-127559
[Patent document 8] Japanese Patent Laid-Open Publication No. 2003-121884
[Patent document 9] Japanese Patent Laid-Open Publication No. Hei 8-73223